1. Field of the Invention
This invention relates to an electronic camera equipped with a solid-state electronic image sensing device for sensing the image of a subject and outputting a video signal representing the image of the subject, and to a method of operating the camera.
2. Description of the Related Art
An electronic camera such as a movie-video camera and still-video camera uses a rechargeable battery as the operating power supply. In general, the rechargeable battery is placed in a charging apparatus that is separate from the electronic camera and is charged by the charging apparatus.
There are also cases where an electronic camera is provided with a power generating device such as a solar battery and the camera is charged using this device.
When a camera is additionally provided with a power generating device, however, the camera cannot be reduced in size. Solar batteries, on the other hand, are expensive and lead to higher camera cost.
Accordingly, an object of the present invention to arrange it so that a rechargeable battery can be charged without using a charging device separate from an electronic camera and without newly providing the electronic camera with a power generating device.
According to the present invention, the foregoing object is attained by providing an electronic camera equipped with a solid-state electronic image sensing device for sensing the image of a subject and outputting a video signal representing the image of the subject, comprising a power-supply switch for controlling a power supply to turn the power supply on and off; a power-supply switch discrimination device (a power-supply switch discrimination means) for determining whether the power-supply switch has been turned off; a charging circuit for charging a rechargeable battery; and a charging control device (charging control means), responsive to a determination by the power-supply switch discrimination device that the power-supply switch has been turned off, for controlling the charging circuit so as to charge the rechargeable battery using signal charge that has accumulated in the solid-state electronic image sensing device.
The present invention provides also a method of controlling the operation of the above-described electronic camera. Specifically, the invention provides a method of controlling the operation of an electronic camera equipped with a solid-state electronic image sensing device for sensing the image of a subject and outputting a video signal representing the image of the subject, comprising the steps of determining whether a power-supply switch, which is for controlling a power supply to turn the power supply on and off, has been turned off, and, in response to turning off of the power-supply switch, charging a rechargeable battery using signal charge that has accumulated in the solid-state electronic image sensing device.
In accordance with the present invention, the rechargeable battery is charged, when the power-supply switch is turned off, using signal charge that has accumulated in the solid-state electronic image sensing device that sensing the image of the subject. The various circuits in the electronic camera are driven by the rechargeable battery thus charged.
Thus, the rechargeable battery of an electronic camera can be charged without newly providing the camera with a power generating device. Since the solid-state electronic image sensing device is already provided in the electronic camera for the purpose of image sensing, the rechargeable battery can be charged without using means that would impede miniaturization of the camera.
When a diaphragm has been provided to limit the quantity of light that impinges upon the solid-state electronic image sensing device, it is preferred that the diaphragm be opened as a result of turning off the power-supply switch. This is because increasing the quantity of light that impinges upon the solid-state electronic image sensing device makes it possible to charge the rechargeable battery more efficiently.
When a mechanical shutter has been provided to limit the length of time during which light impinges upon the solid-state electronic image sensing device, it is preferred that the mechanical shutter be opened as a result of turning off the power-supply switch. This allows light to impinge upon the solid-state electronic image sensing device.
It is preferred that the electronic camera be further provided with a taking lens for forming the image of a subject on a light-receiving surface of the solid-state electronic image sensing device; a focusing mechanism for controlling the taking lens so as to focus the image of the subject on the light-receiving surface of the solid-state electronic image sensing device; and a device for controlling the focusing mechanism, in response to turning off of the power-supply switch, in such a manner that the image of the subject is formed at infinity. The reason for this is that when the rechargeable battery is charged, the light source for charging is considered to be at infinity, thereby raising the efficiency with which light is received.
In a preferred embodiment, a light-transmitting window is formed in the back side of the electronic camera, a light shielding member is made freely attachable to the window, and the underside of the solid-state electronic image sensing device is fixed to the window via a transparent substrate.
Light impinges from the underside of the solid-state electronic image sensing device via the window and signal charge accumulates in the solid-state electronic image sensing device. The efficiency with which signal charge accumulates in the solid-state electronic image sensing device is improved.
Further, it is preferred that the light shielding member be provided with a display device for displaying the image of the subject represented by the video signal output from the solid-state electronic image sensing device.
The light shielding member may be removably attached not only to the back side of the electronic camera but also to the front side of the electronic camera.
Such components as the taking lens and solid-state electronic image sensing device with which the electronic camera is provided can be protected by the light shielding member.
An arrangement may be adopted in which, when the light shielding member has been provided with the display device, the side of the light shielding member having the display device is faced to the outside or to the inside of the camera.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.